The present application is based on Japanese Patent Application No 2000-345216, the entire contents of which are incorporated herein by reference.
1. Field of the Invention
The present invention relates to improvements in a motor rotating a rotor while urging the rotor in the axial direction.
2. Related Art
FIG. 2 shows the conventional structure of a rotor portion for a motor that rotates a rotor 52 while urging a shaft 51 to one side in the axial direction (a direction of the arrow X1 in FIG. 2). The shaft 51 of the rotor 52 is rotatably supported at two places by metal bearings (not shown). One of the two metal bearings for bearing the shaft 51 is attached to the fixture such as a motor case. And the metal bearing attached to this fixture also serves as a thrust pad for receiving one face of the rotor 52 that is urged to one side in the axial direction owing to an urging force.
The motor rotating the rotor 52 while urging it to one side in the axial direction are usually provided with a plurality of washers 53 including a spring washer for urging the rotor 52 to the side of the bearing that is attached to the fixture. That is, the plurality of washers 53 are disposed between an end portion of a main body 52a of the rotor 52 and the bearing not acting as the thrust pad, in which one or two of the plurality of washers 53 are composed of a washer having resilient nature. Thereby, the rotor 52 is pressed to the side of the bearing serving as the thrust pad, and rotates at a predetermined location.
The motor of this type as described above has a structure of rotating the rotor 52 while urging it onto the bearing, using a spring force of the washer 53, to make the rotational position of the rotor 52 relative to a stator (not shown) unchanged on the side where the rotor is urged. However, it is required to dispose a plurality of washers 53 to reduce the friction and wear in various parts. As a result, the dimensional tolerances of the thickness of washers 53 are accumulated, and the positional accuracy of the rotor 52 with respect to the bearing is not always excellent. Consequently, there is a problem that the urging force is greatly dispersed.
Also, the fixture to which the bearing also serving as the thrust pad is attached and the stator are separately provided. Therefore, a dimensional error or attaching error may occur between the fixture and the stator. As a result, the bearing also serving as the thrust pad and acting as the rotational positional regulation part of the rotor has a poor positional accuracy with respect to the stator, leading to a problem that the positional accuracy of rotation of the rotor 52 with respect to the stator is further aggravated.
In the light of the above problems, it is an object of the present invention to provide a motor rotating a rotor in a state of urging the rotor to one bearing side, thereby improving the positional accuracy of rotation of the rotor with respect to a stator and stabilizing an urging force.
In order to accomplish the above object, the present invention provides a motor having an urging member for urging a rotor disposed oppositely to a stator in the axial direction, the motor rotating the rotor in a state under an urging force of the urging member, characterized in that a positional regulation part for regulating the position of the rotor in a thrust direction under the urging force is integrally provided in a coil bobbin made of resin which has metallic stator cores making up the stator formed by insert molding. Therefore, the positional accuracy between the positional regulation part for regulating the thrust position of the rotor and the parts making up the stator, specifically, the stator core and the coil bobbin, can be easily attained, whereby the positional accuracy of rotation of the rotor with respect to the stator is made better. Therefore, the output torque is improved.
Further, the invention provides the motor characterized in that a bearing for rotatably receiving one end of a shaft of the rotor is provided as a slide bearing that is movable in the axial direction, in which a holding portion for holding the slide bearing movably in the axial direction is provided integrally with the coil bobbin, and the urging member is attached to the holding portion. Therefore, the positional accuracy of holding the urging member for urging the slide bearing for receiving the rotor with respect to the coil bobbin is assured, thereby making it easier to control the urging force to urge the rotor. As a result, the rotor is not pressed against the positional regulation part too strongly, or too weakly, and thereby can be rotated in a state of the excellent positional accuracy.
Also, the invention provides the motor characterized in that the positional regulation part is provided in a bearing for bearing the other end of the shaft of the rotor. Therefore, the structure is simplified and more easily manufactured.
Also, the invention provides the motor characterized in that the positional regulation part accepts indirectly an urging force of the urging member via a washer made of resin. Therefore, the positional regulation part formed integrally with the coil bobbin made of resin and the washer made of resin slide with each other, resulting in less sliding loss.
Further, the invention provides the motor characterized in that the other end of the shaft of the rotor is protruded from the bearing, and a lead screw portion is formed in the protruded portion. Conventionally, the motor of this type has, on one end of the stator, the bearing and the urging means for urging the rotor from one end to the other end of the stator, with a U-shaped frame connected to the other end of the stator. The bearing is placed on the opposite side of a connected portion of this frame with the stator to accept the urging force of the urging means. In this manner, when the bearing is disposed via the frame, a piling error of the frame is added, so that the axial accuracy in the thrust direction is naturally worse. In this invention, the positional regulation part is provided in the bearing for receiving the other end portion of the shaft of the rotor, whereby the axial accuracy in the thrust direction can be attained. Also, since the U-shaped frame is not necessitated, the structure can be made compact, and has a greater degree of freedom in design without imposing restrictions on the mounting space on other devices.